RF shield spray on (inside plastic enclosure) how to ground?

Does anyone have any insight or suggestions on how to connect ground to the metallic shield (spray on style that is applied to inside of plastic enclosures to help with radiated emissions)

Spring contacts, screws, adhesive copper tape, conductive gaskets...

Fvm,

I will try the conductive foam from Laird.

Thank you.

Are you trying to shield E fields (E or H fields? What frequency?

Keep in mind conductive spray is very thin and sparse and limited effectiveness depends heavily on coating thickness and lid seals especially which can act as great antenna. e.g. 1~2mil required or equivalent to 1 oz copper thickness.

A shorted scope probe loop to Spectrum Analyzer works best for cheap near field tests on emissions or a coax with a small loop and keep gap smaller than loop diameter for sensing.

So even if you have a perfect shield on all surfaces the box seams can become strong slot radiators of harmonics, so test it. Often a tinned brass shield on board works better with solder tabs and other times, its not the box that radiates but the long IO cables connected to it. In that case, LPF on interface lines will reduce emissions. THis can be ferrite CM choke and/or feedthru caps in connectors or many other methods.

The circuit should be fairly benign because it's low power and low frequency (fundamental noise will be under 150kHz). I expect the cable will be more problematic.

Thank you.

Jester said:

The circuit should be fairly benign because it's low power and low frequency (fundamental noise will be under 150kHz). I expect the cable will be more problematic.

Thank you.

Click to expand...

I tested many HDD's in the 80's at outdoor FCC test sites and came to the same conclusion. The ribbon cable with interleaved grounds still radiated all the harmonics of the 10MBps data stream.
A ferrite sleeve around each I/O cable either torroid or flat ferrite bar, may work best.

Any scope or SA can verify this with near field probing, using scope probe as loop antenna near cable. Use appropriate ferrite type to absorb CM field which becomes prime unintended radiator. THe cable length increase E field strength. Small box may be very benign at low current unless single ended sync clock/data is driving outwards. Then RLC diff. filter may help as well.

Also there conductive silver epoxy.

Also a conductive trace pen that lays down 'liquid silver'.